1. Field of the Invention
This invention relates to a heat exchanger. More particularly, the present invention can be suitably applied to a radiator for radiating heat, from the cooling water of a water-cooled engine, into the atmosphere.
2. Description of the Related Art
A known heat exchanger has a construction in which a tank made of a resin and core plate bonding tubes constituting a core portion are fixed to one another through a seal member such as a packing (Japanese Unexamined Utility Model Publication No. 61-141593).
FIG. 13 shows an example of a sectional construction of a tank portion of such a heat exchanger. As shown in FIG. 13, a core plate 140 is hermetically fixed to an open end face of a tank 110 through a packing 150 and constitutes a bottom surface 141a on the side of a core portion 130 inside a tank inner space.
A fitting groove portion 143 for fitting the packing 150 is formed in the core plate 140 on the outer periphery of a region forming the bottom surface 141a closer to the center of the core portion 130 (tube 132) than the bottom surface 141a. The packing 150 is fitted into the fitting groove 143 of the core plate 140 and is fixed by caulking to the tank 110 side.
The inner space of the tank portion formed by the tank 110 and the core plate 140 can be sufficiently secured by allowing the caulk-fixing portion with the packing 105 to protrude closer to the center of the core portion 130 than the bottom surface 141a of the core plate 140 even in the tank portion having a connection portion having seal performance.
In the heat exchanger according to the prior art described above, however, a load acts on the tank portion from multiple directions when vibration is applied to the heat exchanger, and stress occurs in the bond portion between the core plate and the tubes.
When a load H in a longitudinal direction of the tube 132 acts on the caulk-fixing portion as shown in FIG. 11, for example, a bending moment M occurs and stress concentrates on the tube bond portion (tube root portion). Because the caulk-fixing portion protrudes closer to the center of the core portion 130 than the bottom surface 141a of the core plate 140, the bending moment M occurs and stress also concentrates on the tube bond portion even when the load V in the direction intersecting at right angles the longitudinal direction of the tube 132 is applied.
When an attempt is made to reduce the thickness of the tube from the existing thickness, the tube is likely to be broken owing to the stress concentration at the bond portion between the tube and the core plate. In other words, a further decrease of the thickness of the tube has been difficult because life of the tube is likely to be reduced.